Electronic component device and method for producing the same

ABSTRACT

In a method for producing an electronic component device, a heat bonding step is performed in a state in which low melting point metal layers including low melting point metals including, for example, Sn as the main component, are arranged to sandwich, in the thickness direction, a high melting point metal layer including a high melting point metal including, for example, Cu as the main component, which is the same or substantially the same as high melting point metals defining first and second conductor films to be bonded. In order to generate an intermetallic compound of the high melting point metal and the low melting point metal, the distance in which the high melting point metal is to be diffused in each of the low melting point metal layers is reduced. Thus, the time required for the diffusion is reduced, and the time required for the bonding is reduced.

BACKGROUND OF THE PRESENT INVENTION

1. Field of the Present Invention

The present invention relates to an electronic component device and amethod for producing the same, and particularly to an electroniccomponent device that includes conductor films including high meltingpoint metals that are bonded to each other using a low melting pointmetal, and a method for producing the same.

2. Description of the Related Art

A known method for producing an electronic component device isillustrated in FIGS. 7-1 to 7-4. FIGS. 7-1 to 7-4 illustrate a processfor bonding a first component 1 and a second component 2 to each otherthat are to be provided in an electronic component device. Such aprocess is described in, for example, Japanese Unexamined PatentApplication Publication No. 2002-110726. The first component 1illustrated in FIGS. 7-1 to 7-4 is, for example, a semiconductor chip asdescribed in Japanese Unexamined Patent Application Publication No.2002-110726 and the second component 2 is, for example, a substrate onwhich a semiconductor chip is mounted.

In a stage before bonding the first component 1 and the second component2 to each other, a first conductor film 3 is formed on the firstcomponent 1 and a second conductor film 4 is formed on the secondcomponent 2 as illustrated in FIG. 7-1. The first and second conductorfilms 3 and 4 include high melting point metals, such as Cu, forexample. On the first conductor film 3, an oxidation preventing film 5including, for example, Au is formed. The oxidation preventing film 5prevents oxidation of the Cu when the first conductor film 3 includes Cuas described above. In contrast, on the second conductor film 4, a lowmelting point metal layer 6 including a low melting point metal having amelting point less than that of the high melting point metal is formed.The low melting point metal layer 6 functions as a bonding material, andincludes, for example, Sn.

In order to bond the first conductor film 3 and the second conductorfilm 4 to each other, heating is performed at a temperature between themelting point of the high melting point metals defining the conductorfilms 3 and 4 and the melting point of the low melting point metaldefining the low melting point metal layer 6 while arranging the firstconductor film 3 and the second conductor film 4 so as to face eachother with the low melting point metal layer 6 being interposedtherebetween as illustrated in FIG. 7-1. As a result, first, Au definingthe oxidation preventing film 5 dissolves in the low melting point metallayer 6, whereby the state illustrated in FIG. 7-2 is achieved.

When the heating is further continued, the high melting point metalsdefining the first and second conductor film 3 and 4 are diffused in thelow melting point metal layer 6 to form an intermetallic compound of thehigh melting point metals and the low melting point metal. Then, asillustrated in FIG. 7-3, intermetallic compound layers 7 are formedbetween each of the first and second conductor films 3 and 4 and the lowmelting point metal layer 6. Then, finally, the low melting point metallayer 6 disappears, and a bonding portion 8 in which the first conductorfilm 3 and the second conductor film 4 are bonded to each other throughthe intermetallic compound layer 7 is formed as illustrated in FIG. 7-4.

The low melting point metal layer 6 has a function of compensating forvariations in the spacing between the first conductor film 3 and thesecond conductor film 4. Therefore, the low melting point metal layer 6must have a thickness greater than a minimum thickness. However, as thethickness of the low melting point metal layer 6 increases, the timerequired to diffuse the high melting point metal in the low meltingpoint metal layer 6 increases, which results in a problem of reducedproductivity.

In contrast, when the low melting point metal layer is thin in order tosolve this problem, the ability to compensate for variations in thespacing between the first conductor film 3 and the second conductor film4 is reduced, which results in another problem of a poor bonding portionbeing produced.

Moreover, it is known that the intermetallic compound formed in theintermetallic compound layer 7 is relatively hard and fragile ascompared to pure metals. For example, intermetallic compounds producedby combining Cu and Sn, Cu₆Sn₅, Cu₃Sn, etc., are mentioned. However,when the diffusion amount of Cu in Sn is not sufficient, Cu₆Sn₅, whichis particularly fragile among the intermetallic compounds listed above,is likely to be produced. When a stress caused by, for example, thermalexpansion differences occurs between the first component 1 and thesecond component 2, the distortion cannot be absorbed, and thus,cracking occurs in a portion at which Cu₆Sn₅ is produced, whichsometimes causes poor conduction.

In contrast, in order to shorten the time required to bond the firstconductor film 3 and the second conductor film 4, Japanese UnexaminedPatent Application Publication No. 2007-19360 has proposed a method asillustrated in FIG. 8. FIG. 8 is a figure corresponding to FIG. 7-1. InFIG. 8, components that are equivalent to those illustrated in FIGS. 7-1to 7-4 are designated by the same reference characters, and theduplicate descriptions thereof are omitted.

Referring to FIG. 8, the first conductor film 3 is formed on the firstcomponent 1, and a first low melting point metal layer 6 a is formed onthe first conductor film 3. In contrast, the second conductor film 4 isformed on the second component 2, and a second low melting point metallayer 6 b is formed on the second conductor film 4. Then, a metal powder9 including a high melting point metal is provided on, for example, thefirst low melting point metal layer 6 a.

To bond the first component 1 and the second component 2 to each other,heating is performed while the first and second low melting point metallayers 6 a and 6 b are arranged with the metal powder 9 interposedtherebetween and then the first conductor film 3 and the secondconductor film 4 are arranged to face each other with the low meltingpoint metal layers 6 a and 6 b interposed therebetween. Thus, the highmelting point metal is diffused in each of the low melting point metallayers 6 a and 6 b not only from the first and second conductor films 3and 4, but also from the metal powder to form an intermetallic compound.Therefore, the time required to diffuse the high melting point metalthroughout the low melting point metal layers 6 a and 6 b can bereduced.

However, according to the method illustrated in FIG. 8, when the supplyamount of the metal powder 9 varies, it becomes difficult to uniformlygrow the intermetallic compound from the interface between the first andsecond low melting point metal layers 6 a and 6 b. When Cu is used asthe high melting point metal and Sn is used as the low melting pointmetal and the supply amount of the metal powder 9 is not sufficient toform Cu₃Sn, fragile Cu₆Sn₅ is likely to be formed and, due to the samereasons as described in Japanese Unexamined Patent ApplicationPublication No. 2002-110726 above, cracking is likely to occur, whichcauses poor conduction.

SUMMARY OF THE PRESENT INVENTION

To overcome the problems described above, preferred embodiments of thepresent invention provide a method for producing an electronic componentdevice in which a fragile intermetallic compound is not produced and anelectronic component device produced by the method.

A method for producing an electronic component device according to apreferred embodiment of the present invention includes a step ofindividually preparing a first component on which a first conductor filmincluding a first high melting point metal is formed and a secondcomponent on which a second conductor film including a second highmelting point metal is formed, a step of forming a low melting pointmetal layer including a low melting point metal having a melting pointless than that of the first and second high melting point metals on atleast one of the first and second conductor films, and a heat bondingstep of, while the first conductor film and the second conductor filmare facing each other with the low melting point metal layer beinginterposed therebetween, performing heating at a temperature between themelting points of the first and second high melting point metals and themelting point of the low melting point metal to form an intermetalliccompound of the first and second high melting point metals and the lowmelting point metal, thereby forming a bonding portion in which thefirst conductor film and the second conductor film are bonded to eachother.

In order to solve the above-described problems, a preferred embodimentof the present invention has the following features.

First, the method for producing an electronic component device accordingto a preferred embodiment of the present invention preferably furtherincludes a step of forming a high melting point metal layer includingthe same or substantially the same high melting point metal as eitherone of the first and second high melting point metals so as to contactthe low melting point metal layer. In the low melting point metal layerforming step described above, the low melting point metal layer isformed such that the high melting point metal layer is sandwichedbetween the low melting point metal layers in the thickness direction inthe heat bonding step described above.

The high melting point metal layer formed in the high melting pointmetal layer forming step preferably has a thickness such that the highmelting point metal is supplied in an amount greater than the amountconsumed during the formation of the intermetallic compound. The heatbonding step is preferably performed so that the intermetallic compoundis produced while leaving a portion of the high melting point metallayer at the bonding portion.

Preferably, the first high melting point metal and the second highmelting point metal described above are the same or substantially thesame. In this case, when the high melting point metal includes Cu as themain component, the low melting point metal includes Sn as the maincomponent, and the intermetallic compound to be produced is Cu₃Sn,preferred embodiments of the present invention are particularlyadvantageous.

In the above-described preferred embodiment, by performing the lowmelting point metal layer forming step and the high melting point metallayer forming step, the low melting point metal layer including Sn asthe main component is preferably formed on the first conductor filmincluding Cu as the main component and, in contrast, the low meltingpoint metal layer including Sn as the main component is preferablyformed on the second conductor film, the high melting point metal layerincluding Cu as the main component is preferably formed on the lowmelting point metal layer, and then the low melting point metal layerincluding Sn as the main component is preferably formed on the highmelting point metal layer, in this order.

When the first component is a main substrate on one principal surface ofwhich an electronic circuit formation portion and a first sealing framesurrounding the electronic circuit formation portion are formed, thesecond component is a cap substrate on one principal surface of which asecond sealing frame to be bonded to the first sealing frame is formed,the first sealing frame is defined by the first conductor film, and thesecond sealing frame is defined by the second conductor film, the methodfor producing an electronic component device according to variouspreferred embodiments of the present invention are advantageouslyutilized to bond the first sealing frame and the second sealing frame toeach other.

A first connecting electrode is preferably formed at a position on theone principal surface of the main substrate and is surrounded by thefirst sealing frame, a second connecting electrode is preferably formedat a position on the one principal surface of the cap substrate andsurrounded by the second sealing frame, and a process for electricallyconnecting the first connecting electrode and the second connectingelectrode to each other is preferably performed simultaneously with theheat bonding process.

In the method for producing an electronic component device according tovarious preferred embodiments of the present invention, a firstaggregate substrate and a second aggregate substrate individuallyproviding a plurality of the first and second components are preferablyprepared, and the low melting point metal layer forming step, the highmelting point metal layer forming step, and the heat bonding step maypreferably be performed on the first and second aggregate substrates. Inthis case, in order to produce a plurality of the first and secondcomponents, a step of dividing the first and second aggregate substratesis preferably performed after the heat bonding process.

Preferred embodiments of the present invention are also directed to anelectronic component device including the following features that can beadvantageously produced by the production methods according to variouspreferred embodiments of the present invention.

An electronic component device according to a preferred embodiment ofthe present invention includes a first component on which a firstconductor film including a first high melting point metal is provided, asecond component on which a second conductor film including a secondhigh melting point metal is provided, and a bonding portion arranged tobond the first conductor film and the second conductor film to eachother. The bonding portion includes a first intermetallic compound layerincluding an intermetallic compound of the first high melting pointmetal and a low melting point metal having a melting point less thanthat of the first and second high melting point metals, a secondintermetallic compound layer including an intermetallic compound of thesecond high melting point metal and the low melting point metal, and ahigh melting point metal layer that is disposed between the first andsecond intermetallic compound layers and that includes either one of thefirst and second high melting point metals.

According to the method for producing an electronic component deviceaccording to various preferred embodiments of the present invention, thelow melting point metal layer is preferably provided with a sufficientthickness such that variations in the spacing between the firstconductor film and the second conductor film is sufficiently compensatedfor, and, in the heat bonding process, the high melting point metallayer is sandwiched between the low melting point metal layers in thethickness direction, i.e., the high melting point metal layer isdisposed at the middle in the thickness direction of the low meltingpoint metal layers as a bonding material. Thus, the distance in whichthe high melting point metal is to be diffused in the low melting pointmetal layers can be decreased, and, in accordance therewith, the timerequired to diffuse the same can be reduced. As a result, the efficiencyof the heat bonding process can be significantly improved.

The high melting point metal layer preferably has a thickness such thatthe high melting point metal can be supplied in an amount greater thanthe amount consumed during the formation of the intermetallic compound,and thus, the high melting point metal can be sufficiently supplied intothe low melting point metal layer. Therefore, when both of the first andsecond high melting point metals include Cu as the main component andthe low melting point metal includes Sn as the main component, Cu in asufficient amount to form Cu₃Sn as the intermetallic compound can beprovided. Thus, the formation of Cu₆Sn₅, which is particularly fragileamong the intermetallic compounds, is reliably prevented. Therefore,even when a stress caused by, for example, thermal expansiondifferences, occurs between the first component and the secondcomponent, the occurrence of cracking caused by the distortion, whichresults in poor conduction, is reliably prevented.

Moreover, in particular, it takes a long time to diffuse Sn in Cu, andthus, the above-described effect of shortening the time is particularlyadvantageous when the high melting point metal includes Cu as the maincomponent and the low melting point metal includes Sn as the maincomponent.

When the high melting point metal includes Cu as the main component andthe low melting point metal includes Sn as the main component, a lowmelting point metal layer including Sn as the main component ispreferably provided on the first conductor film including Cu as the maincomponent and, in contrast, when a low melting point metal layerincluding Sn as the main component is preferably provided on the secondconductor film including Cu as the main component, a high melting pointmetal layer including Cu as the main component is preferably provided onthe low melting point metal layer, and then a low melting point metallayer including Sn as the main component is preferably provided on thehigh melting point metal layer, in this order. Thus, at each of thefirst conductor film side and the second conductor film side, both thehigh melting point metal layer and the second conductor film eachincluding, as the main component, Cu that is easily oxidized, arecovered with the low melting point metal layer including, as the maincomponent, Sn having a function of preventing oxidation. Therefore, thehigh melting point metal layer including Cu as the main component andthe second conductor film can preferably be advantageously preventedfrom being oxidized without providing an oxidation preventing film, forexample.

When the first component is a main substrate on which a first sealingframe defined by the first conductor film is provided and the secondcomponent is a cap substrate on which a second sealing frame defined bythe second conductor film is provided, preferred embodiments of thepresent invention can be advantageously used to bond the first sealingframe and the second sealing frame to each other while forming a sealedspace between the main substrate and the cap substrate.

In the above-described preferred embodiments, when the first connectingelectrode is formed at a location surrounded by the first sealing frame,the second connecting electrode is formed at the position surrounded bythe second sealing frame, and the first connecting electrode and thesecond connecting electrode are electrically connected to each othersimultaneously when the first sealing frame and the second sealing frameare bonded to each other, electrical connection and sealing can besimultaneously performed, thereby increasing the productivity of theelectronic component device.

The first and second components are preferably prepared via the firstand second aggregate substrates, respectively, and the low melting pointmetal layer forming step, the high melting point metal layer formingstep, and the heat bonding step are performed in a state of the firstand second aggregate substrates, the production of a plurality ofelectronic component devices can be performed at the same time. Thus, anincrease in the productivity of the electronic component devices can beachieved. In general, since the aggregate substrate has a wide area andthe in-plane variation in the distance between the sealing frames islikely to be relatively large due to bending of the aggregate substrate,the sealing in the aggregate substrate state may produce poor sealingportions. However, with the method for producing an electronic componentdevice according to various preferred embodiments of the presentinvention, the distance between the sealing frames can be increasedwhile maintaining a relatively short bonding time. Therefore, even whenan in-plane variation occurs, sufficient sealing can be performedthroughout the aggregate substrate surface while compensating for thein-plane variation.

With the electronic component device according to preferred embodimentsof the present invention, the high melting point metal layer ispreferably provided between the first and second intermetalliccompounds. The high melting point metal is softer than the intermetalliccompound. Therefore, even when a stress originating from thermalexpansion differences occurs between the first component and the secondcomponent, the high melting point metal layer acts to reduce the stress,thereby effectively preventing the bonding portion from breaking.

Other features, elements, steps, characteristics and advantages of thepresent invention will become more apparent from the following detaileddescription of preferred embodiments of the present invention withreference to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1-1 to 1-4 are cross sectional views illustrating processesprovided in a method for producing an electronic component deviceaccording to a first preferred embodiment of the present invention.

FIG. 2 is a cross sectional view equivalent to FIG. 1-1 for describing asecond preferred embodiment of the present invention.

FIG. 3 is a cross sectional view equivalent to FIG. 1-1 for describing athird preferred embodiment of the present invention.

FIGS. 4A to 4C are views illustrating a first example of an electroniccomponent device to which preferred embodiments of the present inventioncan be applied; in which FIG. 4A is a cross sectional view of anelectronic component device 31, FIG. 4B is a view illustrating a lowerprincipal surface 34 of a cap substrate 33 illustrated in FIG. 4A, andFIG. 4C is a view illustrating an upper principal surface 35 of a mainsubstrate 32 illustrated in FIG. 4A.

FIG. 5 is a cross sectional view illustrating a second example of anelectronic component device to which preferred embodiments of thepresent invention can be applied.

FIG. 6 is a cross sectional view illustrating a third example of anelectronic component device to which preferred embodiments of thepresent invention can be applied.

FIGS. 7-1 to 7-4 are cross sectional views successively illustratingprocesses to be provided in an example of a known method for producingan electronic component device.

FIG. 8 is a cross sectional views equivalent to FIG. 7-1 for describingan example of a known method for producing an electronic componentdevice.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

FIGS. 1-1 to 1-4 are cross sectional views successively illustratingsteps of a method for producing an electronic component device accordingto a first preferred embodiment of the present invention. FIGS. 1-1 to1-4 illustrate a process for bonding a first component and a secondcomponent 12 to each other that are to be provided in a specificelectronic component device. The first and second components 11 and 12preferably include silicon, glass, or ceramic, for example.

FIG. 1-1 illustrates a state before the first component 11 and thesecond component 12 are bonded to each other. On the first component 11,a first conductor film 13 is formed and on the second component 12, asecond conductor film 14 is formed. The first and second conductor films13 and 14 include first and second high melting point metals,respectively. For simplification of the process, the first and secondhigh melting point metals are preferably the same and, for example,include Cu as the main component.

As an example, the first conductor film 13 including Cu as the maincomponent is formed with a thickness of about 4 μm. However, a filmincluding Ti may preferably be formed with a thickness of about 0.05 μm,for example, as a base film contacting the first component 11 (notillustrated). As another example, the second conductor film 14 includingCu as the main component is formed with a thickness of about 4 μm.However, a film including Ti having a thickness of about 0.05 μm, forexample, may preferably be formed as a base layer contacting the secondcomponent 12 (not illustrated).

On the first conductor film 13, an oxidation preventing film 15including, for example, Au is preferably formed with a thickness ofabout 0.1 μm. The oxidation preventing film 15 prevents oxidation of thefirst conductor film 13 including Cu as the main component.

In contrast, on the second conductor film 14, a first low melting pointmetal layer 16 including a low melting point metal having a meltingpoint less than that of the high melting point metal, such as Cu, forexample, as described above. On the first low melting point metal layer16, a high melting point metal layer 17 including the high melting pointmetal is formed. On the high melting point metal layer 17, a second lowmelting point metal layer 18 including the low melting point metal isfurther formed. The low melting point metal layers 16 and 18 function asa bonding material, and preferably include, for example, Sn as the maincomponent. The high melting point metal layer 17 includes Cu as the maincomponent similar to the conductor films 13 and 14.

As an example, the thickness of the first low melting point metal layer16 including Sn as the main component is preferably adjusted to about 3μm, the thickness of the high melting point metal layer 17 including Cuas the main component is preferably adjusted to about 6 μm, and thethickness of the second low melting point metal layer 18 including Sn asthe main component is preferably adjusted to about 3 μm. The thicknessof the high melting point metal layer 17 is selected so that the highmelting point metal in an amount greater than the amount consumed duringthe formation of an intermetallic compound can be provided in a heatbonding process, which will be described later.

The formation of the conductor films 13 and 14, the oxidation preventingfilm 15, the low melting point metal layers 16 and 18, and the highmelting point metal layer 17 described above are preferably formed usingdeposition, sputtering, or metal plating, for example. Compared to themethod for supplying metal powder described in Japanese UnexaminedPatent Application Publication No. 2002-110726 described above, the filmformation methods listed above facilitate the control of the supplyamount, i.e., a film thickness, and, according to the film formationmethods listed above, variations in the film thickness do not readilyoccur.

Next, the first component 11 and the second component 12 are arrangednear each other and are aligned while the first component 11 and thesecond component 12 are arranged to face each other as illustrated inFIG. 1-1, and then pressurized. In the pressurization, a pressure ofabout 5 MPa to about 10 MPa, for example, is preferably supplied. Bypressurizing, the oxidation preventing film 15 at the side of the firstcomponent 11 and the second low melting point metal layer 18 at the sideof the second component 12 contact each other. However, typically, dueto the variation in the thickness direction, the oxidation preventingfilm 15 and the second low melting point metal layer 18 are in contactwith each other only at a portion thereof.

A heat bonding step of performing heating at a temperature between themelting point of Cu as the high melting point metal and the meltingpoint of Sn as the low melting point metal is performed whilemaintaining the above-described pressurization state. In the heatbonding step, an inert atmosphere, such as a nitrogen atmosphere or avacuum, for example, is preferably applied, and a temperature increaserate is preferably adjusted to 10° C./minute, for example. The meltingpoint of Sn is about 232° C. Thus, the temperature exceeds the meltingpoint and Sn defining the low melting point metal layers 16 and 18melts. In this case, due to the pressurization described above, the lowmelting point metal layers 16 and 18 compensate for variations in thethickness direction while being easily deformed, and the oxidationpreventing film 15 contacts the second low melting point metal layer 18over the surface thereof.

For example, when the temperature reaches about 260° C., the increase intemperature is stopped, and then the temperature is maintained. Whenheated as described above, Au defining the oxidation preventing film 15dissolves and disappears in the molten Sn which defines the second lowmelting point metal layer 18. Thus, as illustrated in FIG. 1-2, thefirst conductor film 13 at the side of the first component 11 contactsthe second low melting point metal layer 18 at the side of the secondcomponent 12.

When the heating is further continued, a phenomenon in which Cu definingthe high melting point metal is diffused in the molten Sn which definesthe low melting point metal, to preferably form an intermetalliccompound of Cu and Sn between the first conductor film 13 and the secondlow melting point metal layer 18, between the second low melting pointmetal layer 18 and the high melting point metal layer 17, between thehigh melting point metal layer 17 and the first low melting point metallayers 16, and between the first low melting point metal layer 16 andthe second conductor film 14. Therefore, as illustrated in FIG. 1-3,intermetallic compound layers 19, 20, 21, and 22 are preferably formedbetween the first conductor film 13 and the second low melting pointmetal layer 18, between the second low melting point metal layer 18 andthe high melting point metal layer 17, between the high melting pointmetal layer 17 and the first low melting point metal layer 16, andbetween the first low melting point metal layer 16 and the secondconductor film 14, respectively.

When the heating described above further continues and the diffusion ofCu in the molten Sn further progresses, the first and second low meltingpoint metal layers 16 and 18 disappear, and, as a result, theintermetallic compound layers 19 and 20 are integrated to form a firstintermetallic compound layer 23 and the intermetallic compound layers 21and are integrated to form a second intermetallic compound layer 24, asillustrated in FIG. 1-4.

Thus, a bonding portion 25 in which the first conductor film 13 and thesecond conductor film 14 are bonded to each other is formed. At thebonding portion 25, the high melting point metal layer 17 partiallyremains. Therefore, at the beginning of the formation thereof, the highmelting point metal layer 17 has a thickness such that the amount of thehigh melting point metal is greater than the amount consumed during theformation of intermetallic compounds defining the second intermetalliccompound layers 23 and 24.

According to the production method described above, the high meltingpoint metal layer 17 is sandwiched in the thickness direction by thefirst and second low melting point metal layers 16 and 18 in the heatbonding step while a thickness with which the variation in the intervalbetween the first conductor film 13 and the second conductor film 14 canbe sufficiently compensated for is provided for the low melting pointmetal layers 16 and 18. Thus, the distance in which the high meltingpoint metal is to be diffused in each of the low melting point metallayers 16 and 18 can be reduced, and, in accordance therewith, the timerequired for the diffusion can be reduced.

After the heat bonding step is completed, the resulting component iscooled at a temperature decrease rate of, for example, about 10°C./minute.

When sufficient Cu is not diffused in the molten Sn, Cu₆Sn₅ is likely tobe produced as the intermetallic compound. Cu₆Sn₅ is hard and fragile,and thus is unsuitable as a bonding material. More specifically, it hasbeen confirmed by an experiment that, when a rupture stress that occurswhen a shearing stress is applied to the bonding portion under atemperature of about 280° C. is measured, a rupture stress of about 62.1MPa is obtained when Cu₆Sn₅ is produced but, when Cu₃Sn is produced, arupture stress of about 230.9 MPa is obtained. Therefore, it isnecessary to sufficiently diffuse Cu in the molten Sn to produce Cu₃Snas the intermetallic compound in the heating and bonding process.

As described above, in order to sufficiently diffuse Cu in the molten Snto generate Cu₃Sn, it is important that the thickness of the highmelting point metal layer 17 including Cu as the main component issufficient and Cu can be sufficiently diffused into Sn.

With respect to each of the conductor films 13 and 14 including Cu asthe main component, the low melting point metal layers 16 and 18including Sn as the main component, and the high melting point metallayer 17 including Cu as the main component, the thickness of the filmsand the layers formed at a film formation rate determined so thatneither non-uniformities nor defects are produced after the formationthereof and the films and the layers can be formed in the shortestamount of time as possible is as follows. The ratio of the totalthickness of the conductor films 13 and 14 including Cu as the maincomponent and the high melting point metal layer 17 to the totalthickness of the low melting point metal layers 16 and 18 including Snas the main component (hereinafter referred to as a “Cu thickness/Snthickness ratio”) is preferably at least about 4:3, for example. Whenthe thicknesses of the first conductor film 13, the second conductorfilm 14, and the high melting point metal layer 17 satisfy the followingrelationship represented by the following expressions, Cu in an amountsufficient to produce Cu₃Sn can be supplied into Sn and, after bonding,all of the first conductor film 13, the second conductor film 14, andthe high melting point metal layer 17 can be made to remain.

(Thickness of First conductor film 13)>4/3×½×(Thickness of Second lowmelting point metal layer 18)

(Thickness of Second conductor film 14)>4/3×½×(Thickness of First lowmelting point metal layer 16)

(Thickness of High melting point metal layer 17)>4/3×½×(Thickness ofFirst low melting point metal layer 16+Thickness of Second low meltingpoint metal layer 18)

As described above, when the thickness of the first conductor film 13 isabout 4 μm, for example, the thickness of the second conductor film 14is about 4 μm, the thickness of the first low melting point metal layer16 is about 3 μm, the thickness of the high melting point metal layer 17is about 6 μm, and the thickness of the second low melting point metallayer 18 is about 3 μm, the total thickness of the conductor films 13and 14 including Cu as the main component and the high melting pointmetal layer 17 is about 14 μm, the total thickness of the low meltingpoint metal layers 16 and 18 including Sn as the main component is about6 μm, and the Cu thickness/S thickness ratio is about 7:3. Thus, Cu inan amount sufficient to produce Cu₃Sn can be supplied into the Sn. Thethickness of the first conductor film 13 is preferably about4/3×½×(Thickness of second low melting point metal layer 18), i.e.,greater than about 2 μm, the thickness of the second conductor film 14is preferably about 4/3×½×(Thickness of First low melting point metallayer 16), i.e., greater than about 2 μm, and the thickness of the highmelting point metal layer 17 is preferably about 4/3×½×(Thickness ofFirst low melting point metal layer 16+Thickness of Second low meltingpoint metal layer 18), i.e., greater than about 4 μm. Thus, afterbonding, all of the first conductor film 13, the second conductor film14, and the high melting point metal layer 17 remain.

Moreover, the thickness of a layer required to supply Cu to be diffusedto the low melting point metal layers 16 and 18 each having a thicknessof about 3 μm is preferably about 4 μm when conforming to theabove-described Cu thickness/Sn thickness ratio. However, at both sidesof each of the low melting point metal layers 16 and 18, the layers (theconductor films 13 and 14 and the high melting point metal layer 17)including Cu as the main component are present. Therefore, a layerhaving a thickness of about 2 μm and including Cu as the main componentmay be present at each side of each of the low melting point metallayers 16 and 18. Thus, in the high melting point metal layer 17 havinga thickness of about 6 μm, an intermetallic compound is produced to adepth of about 2 μm from both surfaces thereof. Thus, the high meltingpoint metal layer 17 including Cu as the main component remains and hasa thickness of about 2 μm.

Moreover, in order to sufficiently diffuse Cu in the molten Sn toproduce Cu₃Sn as described above, a heat retention temperature and aheat retention time in the heat bonding step are also important. Whenthe heat retention temperature and the heat retention time areinsufficient, only Cu₆Sn₅ is generated in some cases. In this case, theformation of Cu₃Sn can be accelerated by further elevating the heatretention temperature or further lengthening the heat retention time.For example, it has been confirmed that when heated and maintained atabout 260° C., a Cu₃Sn layer having a thickness of about 2 μm is formedby heating and maintaining for about 15 minutes.

The temperature to be applied in the heat bonding process is preferablytowards the higher end of a permitted range in the electronic componentdevices. As the heating temperature increases, the growth rate of Cu₃Snincreases, thereby further reducing the time required for bonding.

FIG. 2 is a cross sectional view equivalent to FIG. 1-1 to describe amethod of producing an electronic component device according to a secondpreferred embodiment of the present invention. In FIG. 2, componentsequivalent to those illustrated in FIG. 1 are designated by the samereference characters, and the duplicate descriptions thereof areomitted.

In the preferred embodiment illustrated in FIG. 2, the first component11 is prepared in a state in which the second low melting point metallayer 18 is formed on the first conductor film 13 and the secondcomponent 12 is prepared in a state in which a low melting point metallayer is not formed on the high melting point metal layer 17 and theoxidation preventing film 15 is formed thereon.

In the second preferred embodiment, when the first component 11 and thesecond component 12 are arranged near each other, the heat bonding stepis performed, and Au defining the oxidation preventing film 15 dissolvesin the second low melting point metal layer 18, a cross sectionalstructure that is substantially the same as that illustrated in FIG. 1-2is produced. Therefore, subsequent method steps are the same orsubstantially the same as those of the first preferred embodiment.

FIG. 3 is a cross sectional view equivalent to FIG. 1-1 to describe amethod for producing an electronic component device according to a thirdpreferred embodiment of the present invention. In FIG. 3, componentsequivalent to those illustrated in FIG. 1 are designated by the samereference characters, and the duplicate descriptions thereof areomitted.

According to the third preferred embodiment, the second low meltingpoint metal layer 18 is divided into two portions in the thicknessdirection and is formed at both sides of the first component 11 and thesecond component 12. More specifically, the second low melting pointmetal layer 18 including Sn as the main component is formed on the firstconductor film 13 including Cu as the main component. In contrast, thefirst low melting point metal layer 16 including Sn as the maincomponent is formed on the second conductor film 14 including Cu as themain component, the high melting point metal layer 17 including Cu asthe main component is formed on the first low melting point metal layer16, and the second low melting point metal layer 18 including Sn as themain component is further formed on the high melting point metal layer17.

According to the third preferred embodiment, the first conductor film 13including Cu as the main component is covered with the second lowmelting point metal layer 18 including Sn as the main component. Thus,it is not necessary to form an oxidation preventing film such that theuse of expensive Au can be avoided.

The present invention is described above with reference to the preferredembodiments illustrated in the drawings, but various modifications canbe made within the scope of the present invention.

For example, in the above-described preferred embodiments, Cu ispreferably used as the high melting point metal, but Au, Ag, and Ni, forexample, may be used in addition to Cu. Moreover, the first high meltingpoint metal defining the first conductor film 13 and the second highmelting point metal defining the second conductor film 14 may preferablybe different from each other. Moreover, the high melting point metalsmay preferably be used as a pure metal or as a mixture with a slightamount of additives.

In contrast, in the above-described preferred embodiments, Sn ispreferably used as the low melting point metal, but In, multi-componentSn-base solder, and Pb base solder, for example, may preferably be usedin addition to Sn.

In the preferred embodiments illustrated in the drawings, two layers ofthe low melting point metal layers 16 and 18 that sandwich the highmelting point metal layer 17 are preferably used. For example, three ormore low melting point metal layers may preferably be used, such as alow melting point metal layer/a high melting point metal layer/a lowmelting point metal layer/a high melting point metal layer/a low meltingpoint metal layer/a high melting point metal layer, for example.

The production method according to preferred embodiments of the presentinvention is applied to a method of producing an electronic componentdevice including conductor films including high melting point metalsthat are bonded to each other using a low melting point metal. As suchan electronic component device, filters, oscillators, MEMS (MicroElectro Mechanical Systems) components, etc., may be produced, forexample. As the MEMS components, a gyroscope, an acceleration sensor,etc., may be produced, for example. Hereinafter, the specific structureof an electronic component device according to a preferred embodiment ofthe present invention will be described.

FIGS. 4A to 4C illustrate a first example of such an electroniccomponent device according to a preferred embodiment of the presentinvention. The electronic component device 31 has a cross sectionalstructure as illustrated in 4A and has a main substrate 32 and a capsubstrate 33 facing the main substrate 32 at an interval. The structureof a lower principal surface 34 of the cap substrate 33 is illustratedin FIG. 4B and the structure of an upper principal surface 35 of themain substrate 32 is illustrated in FIG. 4C.

On the upper principal surface 35 of the main substrate 32, anelectronic circuit formation portion 36 and a first sealing frame 37surrounding the electronic circuit formation portion 36 are provided. Ata position on the upper principal surface 35 of the main substrate 32and surrounded by the first sealing frame 37, first connectingelectrodes 38 extending from the electronic circuit formation portion 36are provided.

In contrast, on the lower principal surface 34 of the cap substrate 33,a second sealing frame 39 to be bonded to the first sealing frame 37 isprovided. At a position on the lower principal surface 34 of the capsubstrate 33 and surrounded by the second sealing frame 39, secondconnecting electrodes 40 corresponding to the first connectingelectrodes 38 are provided. On the upper principal surface 41 of the capsubstrate 33, terminal electrodes 42 are provided. The terminalelectrodes 42 are electrically connected to the second connectingelectrodes 40 via through hole conductors 43 arranged so as to penetratethe cap substrate 33 in the thickness direction.

To produce such an electronic component device 31, the production methoddescribed with reference to FIGS. 1-1 to 1-4 may preferably be used. Theequivalent relationship between the electronic component device 31 andthe components illustrated in FIGS. 1-1 to 1-4 is as follows: the mainsubstrate 32 is equivalent to the first component 11 and the capsubstrate 33 is equivalent to the second component 12. The first sealingframe 37 is equivalent to the first conductor film 13 and the secondsealing frame 39 is equivalent to the second conductor film 14. In orderto bond the first sealing frame 37 and second sealing frame 39 to eachother, the method illustrated in FIGS. 1-1 to 1-4 is preferably used. InFIG. 4A, the bonding portion 44.

Preferably, a step of electrically connecting the first connectingelectrodes 38 and the second connecting electrodes 40 to each other isperformed simultaneously with a heat bonding step to bond the firstsealing frame 37 and second sealing frame 39 to each other. In thiscase, in the first connecting electrode and the second connectingelectrode 40, the same or substantially the same cross sectionalstructure as in the case of the first sealing frame 37 and the secondsealing frame 39 may preferably be used.

The main substrate 32 and the cap substrate 33 are prepared as aggregatesubstrates 45 and 46 as illustrated by the phantom lines in FIGS. 4C and4B, respectively. The low melting point metal layer forming step, thehigh melting point metal layer forming step, and the heat bonding stepdescribed above are performed on the aggregate substrates 45 and 46. Inorder to produce a plurality of the main substrates 32 and the capsubstrates 33 from the aggregate substrates 45 and 46, the aggregatesubstrates 45 and 46 may be divided after the heat bonding step.

When the intermetallic compound layer formed at the bonding portion 44includes Cu₃Sn in the electronic component device 31 illustrated inFIGS. 4A to 4C as described above, the electronic circuit formationportion 36 surrounded by the sealing frames 37 and 39 are hermeticallysealed with high reliability because the Cu₃Sn has a dense structure.

The melting point of Cu₃Sn is about 676° C. Thus, even when reflow (peaktemperature: about 260° C.) is applied to surface mount the electroniccomponent device 31, high reliability can be maintained in theelectrical conduction properties and the hermetic sealing properties,while not causing re-melting at the bonding portion 44.

FIGS. 5 and 6 illustrate the second and third examples of the electroniccomponent device according to preferred embodiments of the presentinvention.

An electronic component device 51 illustrated in FIG. 5 includes a lid54 that is bonded to a ceramic package 52 in order to accommodate anelectronic component chip 53 in the ceramic package 52 and seal theelectronic component chip 53. The electronic component chip 53 isflip-chip mounted on the ceramic package 52.

In order to produce such an electronic component device 51, theproduction method described with reference to FIGS. 1-1 to 1-4 maypreferably be used. The equivalent relationship between the electroniccomponent device 51 and the components illustrated in FIG. 1 is asfollows: the ceramic package 52 is equivalent to the first component 11and the lid 54 is equivalent to the second component 12. A firstconductor film 55 that is equivalent to the first conductor film 13 isprovided at the peripheral edge portion of an opening of the ceramicpackage 52 and a second conductor film that is equivalent to the secondconductor film 14 is provided at the bottom surface of the lid 54. Inorder to bond the first conductor film 55 and the second conductor film56 to each other, the method as illustrated in FIGS. 1-1 to 1-4 maypreferably be used. In FIG. 5, the bonding portion 57 is illustrated.

An electronic component device 61 illustrated in FIG. 6 includes anelectronic component chip 63 that is mounted on a substrate 62 and ashield case 64 that is bonded to the substrate 62 to shield and seal theelectronic component chip 63. The electronic component chip 63 ismechanically fixed to the substrate 62 through a bonding material 65 andalso is electrically connected thereto by wire bonding 66.

In order to produce such an electronic component device 61, theproduction method described with reference to FIGS. 1-1 to 1-4 maypreferably be used. The equivalent relationship between the electroniccomponent device 61 and the components illustrated in FIG. 1 is asfollows: the substrate 62 is equivalent to the first component 11 andthe shielding case 64 is equivalent to the second component 12. A firstconductor film 67 that is equivalent to the first conductor film 13 isprovided on the upper surface of the substrate 62 and a second conductorfilm 68 that is equivalent to the second conductor film 14 is providedat the peripheral edge portion of an opening of the seal and case 64. Inorder to bond the first conductor film 67 and the second conductor film68 to each other, the method illustrated in FIGS. 1-1 to 1-4 maypreferably be used. In FIG. 5, the bonding portion 69 is illustrated.

While preferred embodiments of the present invention have been describedabove, it is to be understood that variations and modifications will beapparent to those skilled in the art without departing the scope andspirit of the present invention. The scope of the present invention,therefore, is to be determined solely by the following claims.

1. A method for producing an electronic component device, comprising: astep of individually preparing a first component on which a firstconductor film including a first high melting point metal is formed anda second component on which a second conductor film including a secondhigh melting point metal is formed; a low melting point metal layerforming step of forming a low melting point metal layer including a lowmelting point metal having a melting point less than that of the firstand second high melting point metals on at least one of the first andsecond conductor films; a heat bonding step of, while the firstconductor film and the second conductor film are arranged facing eachother with the low melting point metal layer interposed therebetween,performing heating at a temperature between the melting points of thefirst and second high melting point metals and the melting point of thelow melting point metal to form an intermetallic compound of the firstand second high melting point metals and the low melting point metal,thereby forming a bonding portion at which the first conductor film andthe second conductor film are bonded to each other; and a high meltingpoint metal layer forming step of forming a high melting point metallayer including the same or substantially the same high melting pointmetal as at least one of the first and second high melting point metalsso as to contact the low melting point metal layer; wherein the lowmelting point metal layer forming step includes a step of forming thelow melting point metal layer such that the high melting point metallayer is sandwiched between the low melting point metal layers in athickness direction thereof in the heat bonding step; the high meltingpoint metal layer formed in the high melting point metal layer formingstep has a thickness such that the high melting point metal is suppliedin an amount greater than an amount that is consumed during theformation of the intermetallic compound; and the heat bonding step isperformed so that the intermetallic compound is produced while a portionof the high melting point metal layer remains at the bonding portion. 2.The method for producing an electronic component device according toclaim 1, wherein the first high melting point metal and the second highmelting point metal are the same or substantially the same.
 3. Themethod for producing an electronic component device according to claim2, wherein the high melting point metal includes Cu as the maincomponent, the low melting point metal includes Sn as the maincomponent, and the intermetallic compound is Cu₃Sn.
 4. The method forproducing an electronic component device according to claim 3, wherein,by performing the low melting point metal layer forming step and thehigh melting point metal layer forming step, the low melting point metallayer including Sn as the main component is formed on the firstconductor film including Cu as the main component, and the low meltingpoint metal layer including Sn as the main component is formed on thesecond conductor film including Cu as the main component, the highmelting point metal layer including Cu as the main component is formedon the low melting point metal layer, and then the low melting pointmetal layer including Sn as the main component is formed on the highmelting point metal layer, in that order.
 5. The method for producing anelectronic component device according to claim 1, which is used to bonda first sealing frame and a second sealing frame to each other; whereinthe first component is a main substrate on one principal surface ofwhich an electronic circuit formation portion and a first sealing framesurrounding the electronic circuit formation portion are formed and thesecond component is a cap substrate on one principal surface of which asecond sealing frame to be bonded to the first sealing frame is formed;and the first sealing frame is defined by the first conductor film andthe second sealing frame is defined by the second conductor film.
 6. Themethod for producing an electronic component device according to claim5, wherein a first connecting electrode is formed on the one principalsurface of the main substrate and surrounded by the first sealing frame,a second connecting electrode is formed on the one principal surface ofthe cap substrate and surrounded by the second sealing frame, and a stepof electrically connecting the first connecting electrode and the secondconnecting electrode to each other is performed simultaneously with theheat bonding step.
 7. The method for producing an electronic componentdevice according to claim 1, wherein the step of individually preparingthe first and second components includes a step of preparing a firstaggregate substrate and a second aggregate substrate individuallyproviding a plurality of the first and second components, the lowmelting point metal layer forming step, the high melting point metallayer forming step, and the heat bonding step are performed on the firstand second aggregate substrates, and, in order to produce the pluralityof the first and second components from the first and second aggregatesubstrates, a step of dividing the first and second aggregate substratesis performed after the heat bonding step.
 8. An electronic componentdevice, comprising: a first component on which a first conductor filmincluding a first high melting point metal is provided; a secondcomponent on which a second conductor film including a second highmelting point metal is provided; and a bonding portion arranged to bondthe first conductor film and the second conductor film to each other;wherein the bonding portion includes a first intermetallic compoundlayer including an intermetallic compound of the first high meltingpoint metal and a low melting point metal having a melting point lessthan that of the first and second high melting point metals, a secondintermetallic compound layer including an intermetallic compound of thesecond high melting point metal and the low melting point metal, and ahigh melting point metal layer that is arranged between the first andsecond intermetallic compound layers and that includes one of the firstand second high melting point metals.